Hydraulic brake system

ABSTRACT

A hydraulic brake system for vehicles with a brake pressure generator unit which is operable by introducing an actuating force by way of an actuating device that includes a first hydraulic chamber having a volume which decreases when the brake pressure generator unit is actuated, out of which pressure fluid volume is displaced due to the volume decrease and to which wheel brakes are connected by way of a first hydraulic connection, wherein a pump is arranged which is capable of delivering the pressure fluid volume displaced out of the first hydraulic chamber due to the volume decrease into the wheel brakes. The first hydraulic chamber includes an elastic device by which a force/travel characteristic curve is determined in the actuating device when an actuating force is introduced.

TECHNICAL FIELD

The present invention relates to a hydraulic brake system for vehicleswith a brake pressure generator unit which is operable by introducing anactuating force by way of an actuating device that includes a firsthydraulic chamber having a volume which decreases when the brakepressure generator unit is actuated, out of which pressure fluid volumeis displaced due to the volume decrease and to which wheel brakes areconnected by way of a first hydraulic connection, wherein a pump isarranged which is capable of delivering the pressure fluid volume intothe wheel brakes that is displaced out of the first hydraulic chamberdue to the volume decrease.

BACKGROUND OF THE INVENTION

Hydraulic brake systems with hydraulic boosters gain in usage intechnical engineering. This applies in particular to boosters inautomotive vehicles where an objective is that the boosters beingmounted have a very compact design. In addition, the vacuum boosterspreviously used in practice are frequently no longer applicableeffectively because they require considerable space and do not providethe vacuum needed for boosting in modern vehicles.

Hydraulic boosters known from the art are either comparativelycomplicated and permit an only relatively inaccurate control, or theycause considerable reactions to the actuating device, e.g., the brakepedal, and hence impart an uncomfortable pedal feeling to the driver.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to overcome the shortcomings ofbrake systems of this type and to reduce reactive effects of thehydraulic pressure increase or pressure decrease on the actuatingdevice.

This object is achieved by the combination of features to be gatheredfrom the characterizing portion of claim 1.

Thus, the present invention principally involves arranging a pump in thefirst hydraulic connection between the first hydraulic chamber of abrake pressure generator unit and the wheel brakes, the said pumpdelivering the pressure fluid volume into the wheel brakes which isdisplaced out of the first hydraulic chamber when an actuating force ofthe actuating device is introduced, and arranging an elastic means inthe first hydraulic chamber, for reproducing a conventionalvolume-pressure characteristic curve of wheel brakes and, thus, forproducing a force-travel characteristic curve or a force-strokecharacteristic curve which imparts a customary and comfortable pedalfeeling to the driver when a brake pedal is used as the actuatingdevice.

The pump causes a difference in pressure between the first hydraulicchamber and the wheel brakes by delivering the displaced volume out ofthe first hydraulic chamber of the brake pressure generator unit. Thus,the pressure in the first hydraulic chamber is advantageously adjustedto pressures near zero bar by means of a pump of a basically continuousdelivery. The result is that the driver mainly feels only the effect ofthe elastic means; the reactive effect on the actuating device, inparticular, a pedal reaction of the brake pressure that developed on thewheel brakes is greatly reduced.

Another advantage can be seen in the design of the brake system which isrelatively simple under technical aspects. Basically, only one pump isrequired in this arrangement for the application of brake pressure tothe wheel brakes. In addition, the pump may be precharged by the volumedisplacement out of the first hydraulic chamber by means of theactuating force of the driver, which is a major improvement of the brakeoperation and, also, a precondition for a reliable operation at lowtemperatures. The system is technically straightforward and, hence,inexpensive because no additional accumulator is needed in the brakesystem of the present invention.

Further, there is no longer a direct basic relationship between theforce-stroke characteristic curve of the actuating device and thevolume-pressure characteristic curve because force and pressure or,respectively, volume and travel are principally adjustable independentlyof one another. This basically permits configuring the boostingcharacteristics of the brake system as it is desired.

According to the present invention, a positive-displacement pump,preferably, a positive-displacement pump of continuous delivery, is usedas a pump. The inlet pressure is boosted by a connected electric motorto an extent until the outlet pressure at the pump corresponds to thedesired boosted pressure. It is especially favorable in a pump of thistype that pressure increase is achieved with little pulsations and atlow noise. Advantageously, the boosting characteristics is freelyselectable due to a corresponding design and control of the pump. Mediumrefraction does not occur within the entire control circuit because boththe brake pressure generator unit and the actuating circuits of thewheel brakes operate hydraulically. Geared pumps, vane-type pumps, andspindle pumps, however, especially pumps with an internal geared wheel,have proved well suited as variable-displacement pumps of continuousdelivery.

The pump is favorably driven by an electric motor, preferably, anon-brush, permanently excited direct-current motor. Further, the saidmotor may be running with no load when brake pressure is not required sothat start-up of the motor is usually not necessary when brake pressureis needed.

According to the present invention, the pump may be a pump with suctioncontrol or suction throttling. In a suction-controlled/suction-throttledpump, the pressure generated by the pump is controlled by the pressurefluid volume flow that is input at the suction side of the pump. Thistype of pump actuation is relatively easy to realize and good to controlcompared to a clocked actuation. The suction control of the pumpprovides the advantage that the energy is optimally used because thepump is loaded only to a degree that is just required for pressureincrease.

The pump may also be configured as a bidirectionally delivering orreversing pump according to the present invention, permitting both apressure increase in the direction of the wheel brakes and a pressuredecrease of the pressure applied to the wheel brakes by the pump in anactive manner.

According to the present invention, a second hydraulic connection isplaced between the first hydraulic chamber and the wheel brakes andhouses a valve, especially a control valve, by which the pressure fluidvolume flow delivered by the pump is adjustable. This provision ensuresa technically relatively simple and inexpensive adjustment of thedesired brake pressure. It is especially favorable that the controlvalve has an analog operation. This renders possible a relativelystraightforward design of the brake system of the present invention. Onthe one hand, the pressure may thus be controlled very accurately and,on the other hand, an analog valve causes only relatively low noise.

According to this invention, there is provision of a non-return valvewhich is operable by the difference in pressure between the firsthydraulic chamber and the wheel brakes and which opens the secondhydraulic connection when excess pressure prevails in the firsthydraulic chamber. It is thereby achieved that the volume displaced bythe driver in a quick brake application is conducted out of the firsthydraulic chamber directly, i.e., past the pump, into the wheel brake.This safeguards a quick brake effect in a period in which the pump, dueto inertia effects, cannot contribute at all or only to a small degree.

The control valve is designed as a member of a hydraulic-mechanicposition follow-up controller according to the present invention, withthe valve position of this position follow-up controller being variabledue to the deformation of the elastic means in the first hydraulicchamber. Thus, pressure control may take place advantageously without anelectronic actuation of the valve.

A third hydraulic connection accommodating a second valve device isprovided between the first hydraulic chamber and a pressure fluid supplyreservoir. This favorably permits an aspiration of brake fluid out ofthe pressure fluid supply reservoir when the volume displaced from thefirst hydraulic chamber is smaller than the volume required for adefined, desired brake pressure.

According to the present invention, the brake pressure generator unitincludes a master brake cylinder with at least one hydraulic chamber(master brake cylinder chamber), preferably, a tandem master brakecylinder with two hydraulic chambers, one master brake cylinder chamberthereof being connected by way of a hydraulic line to a second pistonchamber in which the first hydraulic piston is designed as a separatingpiston, preferably a separating piston with a central valve, and wherebythe elastic means that is arranged in the first hydraulic chamber can beacted upon by pressure force. The separating piston effects a hydraulicseparation of the tandem master brake cylinder circuits from the thirdbrake circuit, wherein the first hydraulic chamber is connected to theenergy supply by the pump, to the connection to the pressure fluidsupply reservoir by way of preferably the central valve, and to therear-wheel brakes by way of preferably normally open valves, and isconnectable to the front-wheel brakes of the vehicle by way ofpreferably normally closed valves. This separation is advantageousbecause upon failure of the brake system, that means upon failure of thepower supply, the total stroke operation of the driver can bedistributed to the pressurization of the front-axle wheel brakes by wayof the tandem master brake cylinder circuits and the pressurization ofthe rear-axle wheel brakes by way of the third brake circuit. Thus, whenthe third brake circuit fails, this concerns only the rear axle, andfailure of another brake circuit causes only failure of the front-axlewheel brakes. A great availability of the brake system is advantageouslyachieved thereby.

In a preferred embodiment of the present invention, the at least onemaster brake cylinder chamber, preferably two master brake cylinderchambers of a tandem master brake cylinder, is/are connected to twopreferably front wheel brakes by way of at least one hydraulic line,preferably two hydraulic lines, into which an electronically operablevalve is inserted, and there is provision of electronically operablevalves between the first hydraulic chamber and the wheel brakes, andelectronically operable valves are arranged between a fourth hydraulicline for the return of pressure fluid out of the wheel brakes. Thisrenders the control of brake pressure easily possible.

According to the present invention, the at least one master brakecylinder chamber, preferably two hydraulic chambers of a tandem masterbrake cylinder, are connected to two preferably front wheel brakes byway of at least one hydraulic line, preferably two hydraulic lines,inserted into which is a separating valve, preferably each oneelectromagnetically operable, normally open separating valve. The firsthydraulic chamber which includes an elastic means is connected to twopreferably rear wheel brakes by way of the one line and succeeding lineportions into which a separating valve, preferably oneelectromagnetically operable, normally open separating valve, isinserted, and the first hydraulic chamber which includes an elasticmeans is connectable to the two preferably front wheel brakes by way ofa line and succeeding line portions, in which a separating valve,preferably each one electromagnetically operable normally closedseparating valve is inserted. This renders a control of the brakepressure on each individual wheel easily possible.

According to the present invention, there is provision of a fourthhydraulic line which can be closed by way of separating valves,preferably electromagnetically operable, normally closed valves, andpermits a return flow of pressure fluid from the wheel brakes into thepressure fluid supply reservoir, preferably by way of a master brakecylinder chamber, in one operating position. This allows a pressuredecrease in a quick and reliable manner.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings (FIGS. 1 to 8),

FIG. 1 is an embodiment of the brake system of the present inventionincluding a first hydraulic chamber with an elastic means and areversible pump.

FIG. 2 is a view of the resulting brake pressure P_(Rad) in the wheelbrake and the actuating travel S of the brake pedal as a function of thepedal force F.

FIG. 3 is an embodiment of the brake system according to the presentinvention with a valve connected in parallel to the pump.

FIG. 4 is a variation using a hydraulic-mechanic position follow-upcontroller.

FIG. 5 is an embodiment of the brake system of the present invention,wherein the brake pressure generator unit includes a tandem mastercylinder.

FIG. 6 is a variation of the embodiment of FIG. 5, wherein the piston ofthe first hydraulic chamber includes a central valve.

FIG. 7 is an embodiment with a tandem master cylinder, wherein ahydraulic-mechanic valve is substituted for the analog valve.

FIG. 8 is a variation of the embodiment shown in FIG. 6 with anadditional valve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The brake system illustrated in FIG. 1 is basically comprised of a brakepressure generator unit 2 that is operable by an actuating pedal 1 andhas a first hydraulic chamber 3 which houses a first piston 4 with acentral valve 5 and to which is assigned an elastic means, preferably aspring 6. By way of a first hydraulic line 7, the first hydraulicchamber 3 is connected to the wheel brakes 8, 9, 10, 11 associated withwhich are rotational speed sensors 12, 13, 14, 15 in this embodiment.Inserted into the first hydraulic line 7 is a pump which is configuredas a bidirectional pump 16′ herein and operated by a motor 17, and inparallel to which a non-return valve 18 is connected by way of a secondhydraulic line 19. Further, the system includes a pressure fluid supplyreservoir 20. For comprehending the present invention, further controlvalves for brake pressure control, as they are e.g. provided in anAnti-Lock Brake System (ABS) device, an Electronic Stability Program(ESP) device, or a Traction Control System (TCS) are not absolutelynecessary and have been omitted.

When the actuating pedal 1 is depressed, a force is applied to thepiston 4, thereby generating a pressure in the first hydraulic chamber3. The pressure fluid flows out of the first hydraulic chamber 3 via theconnected hydraulic line 7 to the pump 16′. When the pump 16′ isswitched on, i.e., when the motor 17 is energized by a control devicenot shown in FIG. 1, it drives the pump 16′. With the help of pump 16′,the inlet pressure is boosted and conducted from the outlet side of thepump 16′ to the wheel brakes 8, 9, 10, 11 by way of the second line 19.In case the pump 16′ is ineffective, the pressure generated in thepressure generator unit 2 can be applied directly to the wheel brakes 8,9, 10, 11. This ensures an auxiliary braking function. It is arrangedfor that the motor 17 drives the pump 16′ only when there is need. Thismay be done by a corresponding gearbox if the motor 17 is constantlyrunning. With the exception of brake operations that require boosting,it is also possible to activate the motor 17 only when the wheel brakes8, 9, 10, 11 shall be acted upon by brake pressure independently of thedriver's request and, thus, of the brake pressure generator unit, forexample, in the case of a TCS or ESP control intervention. Acorresponding design of the central valve 5 renders it possible in theevent of a TCS or ESP control intervention to have pressure fluidaspirated by the pump 16′ from the pressure fluid supply reservoir 20 byway of the central valve 5 and the first hydraulic chamber 3 and tosupply it to the wheel brakes 8, 9, 10, 11. For a reduction of brakepressure, the bidirectionally operating pump 16′ illustrated in FIG. 1is reversed in its direction of operation and will then deliver pressurefluid from the wheel brakes 8, 9, 10, 11 in the direction of thepressure generator unit 2. The pressure fluid may finally propagate byway of the central valve 5 until the pressure fluid supply reservoir 20.

The brake pressure which results in the wheel brake P_(Rad) and theactuating travel of the brake pedal S are illustrated in FIG. 2 as afunction of the pedal force F. The brake pressure P_(Rad) is dependenton the volume displaced from the first hydraulic chamber 3 and thevolume absorption characteristic curve of the wheel brakes 8, 9, 10, 11itself. The pedal-force/pedal-travel characteristic curve is determinedby the characteristic curve of the spring 6. Thepedal-force/pedal-travel characteristic curve is thus adjustable by thespring characteristic curve and the pedal-force/brake-pressurecharacteristic curve by means of the hydraulic configuration of thebrake system and the control of the motor 17 and the pump 16′ withinrelatively wide limits.

The following FIGS. 3 to 8 are described only insofar as there aredifferences compared to FIG. 1 or the respectively preceding Figures.

It becomes apparent from a preferred aspect of the present inventionshown in FIG. 3 that the bidirectional pump 16′ may be replaced by apump 16 having one direction of operation. In this case, a valve 21,preferably an analog valve, is additionally connected in parallel to thepump 16 and the non-return valve 18. The pump inlet side includes anon-return valve 22 that opens in the direction of the pressuregenerator unit 2. A first pressure sensor 23 is arranged in addition inthe first line 7. Herein, valve 21 controls the brake pressure increaseand decrease. For reasons of control technology and for low noiseeffects, valve 21 is advantageously designed as an analog valve.Advantageously, pump 16 may work continuously during a brake operationbecause the volume flow of pressure fluid to the wheel brakes 8, 9, 10,11 is controllable continuously by way of valve 21. The pump 16 may bethe suction control type or suction throttling type. In this case, onlythe volume displaced out of the first chamber 3 of the pressuregenerator unit 2 by way of line 7 is conducted by means of the pump 16into the wheel brakes 8, 9, 10, 11. Thus, a pressure of roughly zero baris basically always adjusted in the first hydraulic chamber 3 accordingto the present invention.

FIG. 4 differs from FIG. 3 in that associated with the brake pressuregenerator unit 2 is a hydraulic-mechanic position follow-up controllerwhich includes a second hydraulic chamber 24 in which a follow-up piston25 is housed. Placed on follow-up piston 25 is a follow-up valve 26allocated to which is an adjusting rod 27 that is in operativeengagement with the first piston 4 and the position of which changesalong with the deformation of the spring 6. The third hydraulic line 7′on the pump outlet side in the direction of the wheel brakes 8, 9, 10,11 leads into a first hydraulic piston chamber 28 separated from thesecond hydraulic chamber 24 by the follow-up piston 25. A fourthhydraulic line 29 leads from the second hydraulic chamber 24 to thewheel brakes 8, 9, 10, 11. Similar to the embodiments describedhereinabove, the pressure fluid is delivered during a braking operationout of the first chamber 3 with the spring 6, through the line 7, to thepump 16 and then, with correspondingly boosted pressure, through thethird line 7′ into the first piston chamber 28. The wheel brakes 8, 9,10, 11 are pressurized by way of line 29 by the pressure fluid volumeconducted from the second hydraulic chamber 24. Herein, the pressure iscontrolled by means of the follow-up valve 26 which is opened by meansof the adjusting rod 27 corresponding to the pressure produced by thepump, with the result that a defined volume of pressure fluid may flowback via a fifth hydraulic line 30 into the pressure fluid supplyreservoir 20, and with the result that the pressure generated in thewheel brakes 8, 9, 10, 11 by way of the follow-up piston 25 and thefourth line 29 is controlled. Further, pump 16 is connected to thepressure fluid supply generator 20 by way of a sixth hydraulic line 31,into which a non-return valve 32 and a throttle 33 are inserted, and byway of a seventh hydraulic line 34. Leakage flows, such as leakage flowsat the follow-up valve 26, which may lead to a loss in pressure fluid inthe first piston chamber 28 can be compensated thereby. Pressurereduction is possible by way of a central valve 35 in the follow-uppiston 25 and the line 30 up to the pressure fluid supply reservoir 20.

In FIG. 5, an embodiment of the present invention is illustrated whereinthe brake pressure generator unit 2 has a tandem master cylinder 36 thatis operable by the brake pedal and basically includes two pressurechambers, i.e., a first master cylinder chamber 39 and a second mastercylinder chamber 40, which are separated from each other by a firstmaster cylinder piston 37 and a second master cylinder piston 38. Eachmaster cylinder piston 37, 38 includes a central valve 41, 42. Theoperation of tandem master cylinders 36 of this type is not explained indetail in the present context because it is well known to the expertskilled in the respective art. A direct application of the wheel brakes8, 9, 10, 11 by means of the pressure produced in the two brake circuitsof the tandem master cylinder 36 takes place especially in emergencysituations, that means in the event of failure of pump 16 or motor 17.By way of an eighth hydraulic line 43, the first master cylinderpressure chamber 39 is connected to the second hydraulic piston chamber44 which is isolated from the first hydraulic chamber 3 that houses theelastic means 6 by the separating piston 64 (see FIG. 6) which includesa central valve 65. Thus, the separating piston 64 effects a hydraulicseparation of the two tandem master brake cylinder circuits from a thirdbrake circuit, wherein the first hydraulic chamber 3 is connected to theenergy supply by the pump 16, to the connection to the pressure fluidsupply reservoir 20 by way of preferably the central valve 65 (see FIG.6), and to the rear-wheel brakes 10, 11 by way of normally open valves47, 48, and is connectable to the front-wheel brakes 8, 9 of the vehicleby way of preferably normally closed valves 45, 46. In FIG. 5, thecorresponding valves are shown which permit an ABS/TCS control of thebrake pressure. The inlet valves 45, 46, 47, 48 which are inserted intothe line portions 7 a, 7 b, 7 c, 7 d leading to the individual wheelbrakes 8, 9, 10, 11 and succeeding the first line 7, and the outletvalves 50, 51, 52, 53 which are arranged in the line portions 49 a, 49b, 49 c, 49 d of a ninth line 49 leading away from the wheel brakes 8,9, 10, 11 are used for this purpose. From the pressure chambers of thefirst master cylinder 39 and second master cylinder 40, a tenth and aneleventh hydraulic line 54 and 55 lead to the wheel brakes 8 and 9 whichare closable by way of valves 56 and 57.

In a normal braking operation, pressure fluid volume is conducted fromthe first master cylinder chamber 39 into the second hydraulic chamber44, and separating piston 64 is moved in opposition to the resistance ofthe spring 6. Corresponding to the movement of the separating piston 64,pressure fluid is also conducted out of the first hydraulic chamber 3and delivered to the wheel brakes 8, 9, 10, 11 by way of line 7, pump16, and subsequent lines 7 a, 7 b, 7 c, 7 d. Inlet valves 45, 46, 47, 48are open then. The outlet valves 50, 51, 52, 53 are closed in a normalbraking operation without ABS control intervention. The control of thesevalves is carried out according to the known methods of electronic brakecontrol systems such as ABS, TCS, and ESP. The brake pressure applied tosecond line 19 is measured by a second pressure sensor 63. All valvesand motor 17 are controlled according to a driver's request for brakingsensed by means of a travel sensor 62 at the actuating pedal 1 and independence on the pressure which is actually measured by the secondpressure sensor 63. A good ‘two-stage reaction device function’ can berepresented by means of the travel sensor signal, this means, a definedtravel/pressure characteristic curve of the system is adjusted, wherebythe controllability of the brake effect in the lower range of brakepressure is improved for the driver. The valves 47 and 48 and 56 and 57,as illustrated herein, are preferably opened in the deenergizedcondition and ensure an emergency brake function in the event of failureof the hydraulic boosting by the pump 16 or the motor 17. The brakepressure may then be conducted from the pressure chambers of the firstand second master cylinder 39, 40 by way of the lines 54, 55 to thewheel brakes 8 and 9, on the one hand, and from the first pressurechamber 3 by way of the line 7 to the wheel brakes 10 and 11 directly byapplication of the brake pedal 1, on the other hand. Thus, all fourwheel brakes 8, 9, 10, 11 can be acted upon by the driver's footpressure as pressure source in the event the system fails. In the eventof failure of the energy supply by the pump, the entire stroke actionprovided by the driver to pressurize the front-axle wheel brakes isenabled by way of the circuits of the tandem master brake cylinder and,for the rear-axle wheel brakes, by way of the third brake circuit due tothe separation of the hydraulic circuits. It is thus ensured that onlythe rear axle is affected in the event of failure of the third brakecircuit and, on the other hand, failure of any other brake circuit(tandem master brake cylinder circuit) may only cause failure of thefront-axle wheel brakes.

FIG. 6 illustrates a design corresponding to FIG. 5 wherein theseparating piston 64 of the first hydraulic chamber 3 includes a centralvalve 5. Further, a damping chamber 58 is integrated in line 7 fordamping pulsations, and a pressure-limiting valve 59 that opens in thedirection of the first hydraulic chamber is arranged in parallel tovalve 21, whereby a quick and reliable reduction of the pressureprevailing at the wheel brakes 8, 9, 10, 11 is achieved by way of theoutlet valves 50, 51, 52, 53. This embodiment reliably ensures a slow orquick pressure increase or decrease in conformity with requirements, anda particularly effective pulsation decoupling of the actuating device 1is additionally achieved. Besides, the wheel brakes of one axle of thevehicle are acted upon evenly, and an angular deviation due to an unevenbrake pressure proportioning is avoided.

To accomplish the brake system of the present invention, only onesingle-circuit pump 16, three control valves 21, 50, 51, and eightswitching valves 45, 46, 47, 48, 52, 53, 56, 57 are necessary in totalin the case of control. A brake system of this type is basicallyappropriate for use in all electronic brake control systems, such asABS, TCS, ESP, HBA (Hydraulic Brake Assistant), or ACC (Automatic CruiseControl). All four wheel brakes 8, 9, 10, 11 are operable by thedriver's force when the system fails. A pressure decrease in a controlphase of an electronic brake control system, for example the ABS, ispossible until zero bar. The control intervention by TCS can be effectedso as to be uncoupled from an actuation by the driver. In the case of anESP control, a hydraulic connection to the pressure fluid supplyreservoir 20 having a sufficiently large cross-section permits a rapidaspiration of pressure fluid so that a quick increase of high brakepressures in the wheel brakes can be realized.

FIGS. 7 and 8 show two embodiments of the present invention wherein thevalve 21 is obviated and its function is performed by ahydraulic-mechanically controlled valve 60. A shut-off valve 61 isadditionally inserted in the brake system shown in FIG. 8, allowing achange-over to independent actuation by the electronic brake controlsystem for the purpose of an active braking operation in accordance witha brake control system such as TCS or ESP.

LIST OF REFERENCE NUMERALS

-   1 actuating pedal-   2 brake pressure generator unit-   3 first hydraulic chamber-   4 first piston-   5 central valve-   6 spring-   7 first hydraulic line-   7′ third hydraulic line-   8 first wheel brake-   9 second wheel brake-   10 third wheel brake-   11 fourth wheel brake-   12 first wheel speed sensor-   13 second wheel speed sensor-   14 first wheel speed sensor-   15 second wheel speed sensor-   16 pump-   16′ bidirectional pump-   17 motor-   18 non-return valve-   19 second hydraulic line-   20 pressure fluid supply reservoir-   21 valve-   22 non-return valve-   23 first pressure sensor-   24 second hydraulic chamber-   25 follow-up piston-   26 follow-up valve-   27 adjusting rod-   28 first hydraulic piston chamber-   29 fourth hydraulic line-   30 fifth hydraulic line-   31 sixth hydraulic line-   32 non-return valve-   33 restrictor-   34 seventh hydraulic line-   35 central valve-   36 tandem master brake cylinder-   37 first master cylinder piston-   38 second master cylinder piston-   39 first master cylinder chamber-   40 second master cylinder chamber-   41 central valve-   42 central valve-   43 eighth hydraulic line-   44 second hydraulic piston chamber-   45 inlet valve-   46 inlet valve-   47 inlet valve-   48 inlet valve-   49 ninth hydraulic line-   50 outlet valve-   51 outlet valve-   52 outlet valve-   53 outlet valve-   54 tenth hydraulic line-   55 eleventh hydraulic line-   56 separating valve-   57 separating valve-   58 damping chamber-   59 pressure-limiting valve-   60 hydraulic-mechanically controlled valve-   61 shut-off valve-   62 travel sensor-   63 second pressure sensor-   64 separating piston-   65 central valve

1-10. (canceled)
 11. Hydraulic brake system, comprising: a brakepressure generator unit which is operable by introducing an actuatingforce by way of an actuating device, wherein said brake pressuregenerator includes a first hydraulic chamber having a volume whichdecreases when the brake pressure generator unit is actuated, out ofwhich a pressure fluid volume is displaced due to the volume decreaseand to which wheel brakes are connected by way of a first hydraulicconnection, a pump coupled to said first hydraulic chamber fordelivering the pressure fluid volume into said set of wheel brakes,wherein said pressure fluid volume is displaced out of the firsthydraulic chamber due to the volume decrease, and wherein the firsthydraulic chamber includes an elastic device disposed therein, whereinsaid elastic device defines force versus travel characteristics in theactuating device when said actuating force is introduced, wherein thebrake pressure generator unit includes a tandem master brake cylinderwith two hydraulic master brake cylinder chambers, one master brakecylinder chamber thereof being connected by way of a hydraulic line to asecond piston chamber in which the elastic device can be acted upon bypressure force by means of a separating piston.
 12. Brake system asclaimed in claim 11, wherein the pump is configured as a bidirectionalpump.
 13. Brake system as claimed in claim 11, wherein a secondhydraulic connection is disposed between the first hydraulic chamber andthe wheel brakes and houses a control valve.
 14. Brake system as claimedin claim 11, the brake system further including a second hydraulicconnection disposed between the first hydraulic chamber and the set ofwheel brakes and houses a control valve, and further including anon-return valve which is operable by the difference in pressure betweenthe first hydraulic chamber and the wheel brakes and which opens thesecond hydraulic connection when excess pressure prevails in the firsthydraulic chamber.
 15. Brake system as claimed in claim 11, the brakesystem further including a second hydraulic connection disposed betweenthe first hydraulic chamber and the set of wheel brakes and houses acontrol valve, wherein the control valve is designed as a part of ahydraulic-mechanical position follow-up controller, wherein the valveposition of this hydraulic-mechanical position follow-up controller isvariable due to a deformation of the elastic means.
 16. Brake system asclaimed in claim 11, wherein a third hydraulic connection accommodatinga second valve is provided between the first hydraulic chamber and apressure fluid supply reservoir.
 17. Brake system as claimed in claim11, wherein the brake pressure generator unit further includes a tandemmaster brake cylinder with two hydraulic master brake cylinder chambers,one master brake cylinder chamber thereof being connected by way of ahydraulic line to a second piston chamber, wherein the elastic devicethat is arranged in the first hydraulic chamber can be acted upon bypressure force by means of a separating piston, wherein a ninthhydraulic line is included which is closed by way of separating valves,each one electromagnetically operable, normally closed valves, andpermits a return flow of pressure fluid from the wheel brakes into thepressure fluid supply reservoir, by way of a master brake cylinderchamber, in one operating position.
 18. Brake system as claimed in claim11, the brake system further comprising a second hydraulic connection isdisposed between the first hydraulic chamber and the wheel brakes andhouses a control valve, wherein the control valve is an analog valve.